When it comes to bunion surgery, we all have our “favorite” technique. Not only do we have a comfort level with the technique, we feel we can use this technique or simple modifications thereof to fix most bunion deformities. In this blog, I want to remind you of an old procedure that has become revitalized recently.
The opening base wedge osteotomy of the first metatarsal is indicated for the correction of hallux valgus with a shortened first ray (see figure 1). In the past, the procedure had fallen out of favor due to a number of technical reasons. The most common reason for avoidance of the opening wedge procedure is the difficulty to obtain adequate fixation of the osteotomy. Other reasons include the need to obtain a bone graft, a prolonged period of non-weightbearing, elevatus of the first ray, first metatarsophalangeal joint (MPJ) narrowing and fear of delayed union or nonunion.
When it comes to hallux valgus with larger intermetatarsal angles, surgeons use closing base wedge osteotomies and Lapidus arthrodeses more often than opening wedge osteotomies due to familiarity of those procedures. Moreover, bone grafting is rarely necessary. These methods are successful in the outcome of hallux valgus correction. However, closing base wedge osteotomies and Lapidus arthrodesis procedures may lead to shortening of the first ray. A shortened first ray may lead to lesser metatarsal overload, attributing to (metatarsalgia) second MPJ pain, instability and/or callus development (see figure 2).
It is difficult to avoid metatarsal elevatus in a closing base wedge osteotomy despite eight weeks of cast immobilization. This is probably due to the typical fixation construct of two lag screws across the osteotomy, which does not shield plastic deformation of bone.
New forms of fixation have been designed specifically for the opening base wedge osteotomy. The tibial opening wedge plate system for tibial varum has modifications for the first metatarsal. These fixation devices are plate systems with or without locking screws. Better fixation constructs allow weightbearing to commence earlier and diminish the risk of the complication of first metatarsal elevatus.
A Guide To The Opening Base Wedge Osteotomy Technique
The surgeon should ensure the patient is in a supine position on the table. One may use IV sedation and local anesthesia or a general anesthetic. Achieve hemostasis with a tourniquet or with local administration of epinephrine per surgeon preference. Perform a proximal first ray block with local anesthesia. Identify the location of the first metatarsal cuneiform joint with fluoroscopy and mark it with an ink pen.
The first part of the procedure involves the “bunionectomy,” removing the exostosis and performing the standard lateral release of the first metatarsophalangeal joint. Proceed to carry the incision more proximal to the level of the first metatarsocuneiform joint. Carry dissection down through the subcutaneous tissues and retract the extensor hallucis longus tendon laterally. You will always encounter a fairly large crossing vein that you will need to clamp, cut and tie. I do not reflect the periosteum at the osteotomy site.
Use a 0.062 K-wire as an axis guide and insert it dorsal to plantar at the site of the lateral hinge. The axis guide should be perpendicular to the weightbearing surface to avoid elevatus of the metatarsal. Utilize fluoroscopy to identify the location of the hinge, which should be about 1 to 1.5 cm from the joint. A quick tip to access your location accurately on fluoroscopy is to aim the beam of the X-ray down the K-wire, which is referred to as the “bull’s-eye view” (see figure 3).
Once the location of the hinge is adequate, use a sagittal saw to make a transverse osteotomy to the axis guide, ensuring that you have retracted the extensor tendon dorsally and laterally (see figure 4). Then insert a 10 mm osteotome medially in the osteotomy. A gentle prying motion will open the osteotomy without disrupting the lateral cortex (see figure 5). If necessary, insert a 0.062 K-wire from medial to lateral in the metatarsal head to use as a lever arm (see figure 6).
With your left hand, force the K-wire distally to open the osteotomy. Use your right hand to place the plate over the osteotomy and, with gentle pressure, place the plate “wedge” into the osteotomy. Depending on the size of the deformity, I will usually do a trial with a 3 or 4 mm plate. One can then visualize this on fluoroscopy and select a larger or small size wedge if necessary. Proceed to pre-drill, measure and insert the accompanying, self-tapping screws.
One may employ intraoperative images to assess correction with translocation of the metatarsal head over the sesamoids. Fluoroscopy can confirm screw purchase of the far cortices without violating the metatarsocuneiform joint. (see figure 7).
One may place bone graft material in the remaining gap lateral to the plate wedge. Generally, one can crush the “bunion” exostosis and use it as graft. Usually, more graft is necessary and the surgeon can augment this with whatever allograft he or she has on hand. Finally, evaluate the range of motion and position of the hallux. The surgeon can then perform any other adjunctive procedure (soft tissue or osseous) as deemed necessary. Apply a layered closure and a compression dressing with posterior splint.
Further Pointers On Ensuring Post-Op Success
As surgeons, we are all trying to master the art of bunion surgery every time we enter the operating room. Most of the time we are pleased with the outcome but failures do occur, especially in the long term. Most of us will agree that under-correction and/or recurrence of the deformity is an all too common concern.
The mobility of the first ray is often the reason for inadequate correction. If the first ray is too flexible, we lose our correction of the osteotomy over time. If the first ray is too rigid, it can be difficult to obtain correction on the table. Although there are exceptions, we teach our surgical residents a general rule: if the first ray is very flexible or rigid, do a base wedge osteotomy or Lapidus arthrodesis. Everything else can get an Austin (or equivalent).
Just remember that all bunion deformities are different. Therefore, we cannot treat this deformity simply by drawing angles on X-rays and coming up with a treatment plan.
The opening base wedge osteotomy is again becoming a viable option in the correction of moderate to severe bunion deformities in cases in which there is a short first ray with a large intermetatarsal angle. I will always give it consideration in revision surgery as often there is not much metatarsal head to work with and some shortening may have occurred.
When the right patient meets the inclusion criteria, do not forget about the opening base wedge osteotomy for hallux valgus. There is a learning curve, especially with opening the osteotomy and placing the plate. This is especially the case if you do not have a pair of extra hands in the operating room. If one is too rough, the cortex breaks easily and this becomes a bit of a challenge to handle. Once you get the finesse down, the procedure takes no more time than doing an Austin procedure.